> On Mar 17, 2021, at 9:46 PM, Longpeng (Mike, Cloud Infrastructure Service Product Dept.) <longpeng2@huawei.com> wrote:
> 

[Snip]

> 
> NOTE, the magical thing happen...(*Operation-4*) we write the PTE
> of Operation-1 from 0 to 0x3 which means can Read/Write, and then
> we trigger DMA read again, it success and return the data of HPA 0 !!
> 
> Why we modify the older page table would make sense ? As we
> have discussed previously, the cache flush part of the driver is correct,
> it call flush_iotlb after (b) and no need to flush after (c). But the result
> of the experiment shows the older page table or older caches is effective
> actually.
> 
> Any ideas ?

Interesting. Sounds as if there is some page-walk cache that was not
invalidated properly.